Prevent collision of imported type with exported declarations in current module (#31231)

* check for exported type name for conflict

* refactor baseline tests for import/export name collision

Author: collin5

src/compiler/checker.ts

@@ -31965,7 +31965,7 @@ namespace ts {
         }
 
         function checkAliasSymbol(node: ImportEqualsDeclaration | ImportClause | NamespaceImport | ImportSpecifier | ExportSpecifier) {
-            const symbol = getSymbolOfNode(node);
+            let symbol = getSymbolOfNode(node);
             const target = resolveAlias(symbol);
 
             const shouldSkipWithJSExpandoTargets = symbol.flags & SymbolFlags.Assignment;
@@ -31976,6 +31976,7 @@ namespace ts {
                 // Based on symbol.flags we can compute a set of excluded meanings (meaning that resolved alias should not have,
                 // otherwise it will conflict with some local declaration). Note that in addition to normal flags we include matching SymbolFlags.Export*
                 // in order to prevent collisions with declarations that were exported from the current module (they still contribute to local names).
+                symbol = getMergedSymbol(symbol.exportSymbol || symbol);
                 const excludedMeanings =
                     (symbol.flags & (SymbolFlags.Value | SymbolFlags.ExportValue) ? SymbolFlags.Value : 0) |
                     (symbol.flags & SymbolFlags.Type ? SymbolFlags.Type : 0) |

tests/baselines/reference/mergeWithImportedNamespace.errors.txt

@@ -0,0 +1,13 @@
+tests/cases/compiler/f2.ts(1,9): error TS2440: Import declaration conflicts with local declaration of 'N'.
+
+
+==== tests/cases/compiler/f1.ts (0 errors) ====
+    export namespace N { export var x = 1; }
+    
+==== tests/cases/compiler/f2.ts (1 errors) ====
+    import {N} from "./f1";
+            ~
+!!! error TS2440: Import declaration conflicts with local declaration of 'N'.
+    export namespace N {
+        export interface I {x: any}
+    }

tests/baselines/reference/mergeWithImportedNamespace.js

@@ -5,7 +5,6 @@ export namespace N { export var x = 1; }
 
 //// [f2.ts]
 import {N} from "./f1";
-// partial revert of https://github.com/Microsoft/TypeScript/pull/7583 to prevent breaking changes
 export namespace N {
     export interface I {x: any}
 }

tests/baselines/reference/mergeWithImportedNamespace.symbols

@@ -7,11 +7,10 @@ export namespace N { export var x = 1; }
 import {N} from "./f1";
 >N : Symbol(N, Decl(f2.ts, 0, 8), Decl(f2.ts, 0, 23))
 
-// partial revert of https://github.com/Microsoft/TypeScript/pull/7583 to prevent breaking changes
 export namespace N {
 >N : Symbol(N, Decl(f2.ts, 0, 23))
 
     export interface I {x: any}
->I : Symbol(I, Decl(f2.ts, 2, 20))
->x : Symbol(I.x, Decl(f2.ts, 3, 24))
+>I : Symbol(I, Decl(f2.ts, 1, 20))
+>x : Symbol(I.x, Decl(f2.ts, 2, 24))
 }

tests/baselines/reference/mergeWithImportedNamespace.types

@@ -8,7 +8,6 @@ export namespace N { export var x = 1; }
 import {N} from "./f1";
 >N : typeof N
 
-// partial revert of https://github.com/Microsoft/TypeScript/pull/7583 to prevent breaking changes
 export namespace N {
     export interface I {x: any}
 >x : any

tests/baselines/reference/mergeWithImportedType.errors.txt

@@ -0,0 +1,11 @@
+tests/cases/compiler/f2.ts(1,9): error TS2440: Import declaration conflicts with local declaration of 'E'.
+
+
+==== tests/cases/compiler/f1.ts (0 errors) ====
+    export enum E {X}
+    
+==== tests/cases/compiler/f2.ts (1 errors) ====
+    import {E} from "./f1";
+            ~
+!!! error TS2440: Import declaration conflicts with local declaration of 'E'.
+    export type E = E;

tests/baselines/reference/mergeWithImportedType.js

@@ -5,7 +5,6 @@ export enum E {X}
 
 //// [f2.ts]
 import {E} from "./f1";
-// partial revert of https://github.com/Microsoft/TypeScript/pull/7583 to prevent breaking changes
 export type E = E;
 
 //// [f1.js]

tests/baselines/reference/mergeWithImportedType.symbols

@@ -7,7 +7,6 @@ export enum E {X}
 import {E} from "./f1";
 >E : Symbol(E, Decl(f2.ts, 0, 8), Decl(f2.ts, 0, 23))
 
-// partial revert of https://github.com/Microsoft/TypeScript/pull/7583 to prevent breaking changes
 export type E = E;
 >E : Symbol(E, Decl(f2.ts, 0, 23))
 >E : Symbol(E, Decl(f2.ts, 0, 8), Decl(f2.ts, 0, 23))

tests/baselines/reference/mergeWithImportedType.types

@@ -7,7 +7,6 @@ export enum E {X}
 import {E} from "./f1";
 >E : typeof E
 
-// partial revert of https://github.com/Microsoft/TypeScript/pull/7583 to prevent breaking changes
 export type E = E;
 >E : E
 

tests/cases/compiler/mergeWithImportedNamespace.ts

@@ -4,7 +4,6 @@ export namespace N { export var x = 1; }
 
 // @filename: f2.ts
 import {N} from "./f1";
-// partial revert of https://github.com/Microsoft/TypeScript/pull/7583 to prevent breaking changes
 export namespace N {
     export interface I {x: any}
 }

tests/cases/compiler/mergeWithImportedType.ts

@@ -4,5 +4,4 @@ export enum E {X}
 
 // @filename: f2.ts
 import {E} from "./f1";
-// partial revert of https://github.com/Microsoft/TypeScript/pull/7583 to prevent breaking changes
 export type E = E;